1. Field of the Invention
This invention relates to a non-flammable open-cell cross-linked polyolefin foam and a method for the production thereof.
2. Description of the Prior Art
The open-cell cross-linked polyolefin foam recently developed is inexpensive and excellent in such physical properties as cushioning property, heat-insulating property, and sound absorbing property and, therefore, has been finding extensive utility in various applications including cushioning materials, packing materials, filters, coating applicator, and sound absorbing materials.
Polyolefin resins such as polyethylene and polypropylene are highly flammable and emit intense heat during combustion. This fact has prevented the open-cell polyolefin foams from being used in flooring materials, wall materials, and interior materials for aircraft.
Heretofore, for the production of flame-retardant foams, a method which comprises heating and expanding a foamable polyolefin resin composition incorporating therein an inorganic filler [for example, see Japanese Patent Publication No. SHO 60(1985)-26,500] and a method which comprises heating and expanding a foamable polyolefin resin composition incorporating therein a phosphorus type or halogen type flame-retarding agent [for example, see Japanese Patent Publication No. SHO 48(1973)-9,587, and Japanese Patent Publication No. SHO 58(1983)-5,930], etc. have been adopted.
The method involving the incorporation of an inorganic filler requires the inorganic filler to be incorporated in a large amount into the foamable resin composition for the purpose of imparting the desired flame-retarding property to the produced foam. This method, therefore, incurs difficulty in producing a foam of an expansion ratio of not less than 30 times the original volume and prevents the produced foam from manifesting outstanding flexibility and elongation inherent in a foamed product. On the other hand, the method involving the incorporation of a halogen type flame-retarding agent tends to encounter an increasingly harsh restriction because the flame-retarding agent itself and the gas liberating therefrom are toxic.
In any event, the two methods mentioned above concern production of a closed-cell foam and are not easily adapted for the porduction of an open-cell cross-linked polyolefin foam. This is because the open-cell foam contains the air which promotes combustion in a larger amount than the closed-cell foam and the inorganic filler or flame-retarding agent, even when added to the open-cell foam in the same ratio as to the closed-cell foam, fails to impart a satisfactory flame-retarding property to the open-cell foam. Thus, the open-cell foam is not allowed to acquire the desired flame-retarding property. Besides, the incorporation of the inorganic filler or flame-retarding agent in a large amount prevents the produced open-cell foam from acquiring a satisfactory quality because this foam necessitates very exacting foaming conditions.